In an apparatus for producing a magnetic tape, photographic film, optical functional film or the like, a web is continuously fed from a whole roll. While the web is being fed out, a functional material such as a magnetic material, photosensitive material, optical functional material or the like is coated onto one surface of the web. The web is then dried and wound into a roll form again. Such a producing apparatus is provided with a plurality of rollers for guiding the running web along a predetermined passage.
A device that uses the magnetic tape, photographic film, optical functional film or the like has recently been miniaturized. Along with this trend, the web of these materials is desired to be thinned and smoothed. When the web is thinned and smoothed, however, the rollers slip with respect to the web while conveying the web, and the web may have scratches, wrinkles and the like. In addition, when the web just after being coated with the functional material is conveyed, roller marks may remain on the coated surface, which decreases the yield.
In order to solve these problems, rollers having a peripheral face provided with a spirally extending groove and an upheaval part for conveying a thin web whose thickness is not more than 25 μm are proposed (see Japanese Patent Laid-open Publications No. 8-175727 and 10-77146). In addition, a web guide roller having fine recessed parts is also proposed. An average depth of the recessed parts is 5 μm or more and 50 μm or less, and an occupation area rate of flat parts besides the recessed parts is 50% or more and 70% or less (see Japanese Patent Laid-open Publication No. 2003-146505).
The rollers disclosed in the Japanese Patent Laid-open Publications No. 8-175727 and 10-77146 convey the web having the thickness of not more than 25 μm and on which no functional material is coated. Therefore, the publications do not consider the occurrence of the roller marks which may be generated just after the coating of the functional material on the web.
The web guide roller disclosed in the Japanese Patent Laid-open Publication No. 2003-146505 has the recessed parts formed on the peripheral face thereof by blasting. In the blasting, fine particles, such as aluminasol or glass beads, are blasted toward the roller, therefore the recessed parts may be dispersed randomly. Moreover, the fine particles have variation in size, therefore the depths of the recessed parts are not uniform. Furthermore, the roller cannot maintain the frictional force when the web conveying speed becomes high, and the roller may slip with respect to the web.
During the so-called film production, in which a film is produced from a polymer, the rollers slip with respect to the film while conveying the film, like the rollers slip with respect to the web during the coating process, and the film may have scratches, wrinkles and the like. In the film production according to the solution casting method, a film containing a solvent, a hot film being heated, or the like is conveyed. In the film production according to the melt extrusion method, a film having a temperature as high as approximately a melting point thereof, or the like is conveyed. During the film conveyance, the film itself may have roller marks. Note that the roller marks generated on the film itself during the film production is also referred to as “roller marks” in the following descriptions.